Energy From Reactions

Question 1

What errors could happen in a calorimetry experiment?

Answer 1

Lots of heat is lost of surroundings (not all goes to the water)
Not all of the food/fuel burns.
Water should be stirred (so heat is distributed easily)
Some energy heats the container(not the water)

Question 2

What is an exothermic reaction?

Answer 2

A reaction which gives out energy to the surroundings usually in the form of heat and shown by a rise in temperature.

Question 3

What is an endothermic reaction?

Answer 3

A reaction which takes in energy from the surroundings, usually in the form if eat and shown by a fall in temperature.

Question 4

What happens to bonds in a chemical reaction?

Answer 4

Old bonds are broken ad news bonds are formed.

Question 5

What sort of process is breaking bonds?

Answer 5

Energy must be supplied to break existing bonds so it is an endothermic process.

Question 6

What sort of process is forming bonds?

Answer 6

Energy is released when new bonds are formed so it is an exothermic process.

Question 7

What method can you do to measure the amount of energy released by a chemical reaction?
What reactions does this work for?

Answer 7

Taking the temperature of reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction.
This method works for reactions of solids with water and neutralisation reactions.

Question 8

How do you reduce energy lost o surroundings in a chemical reaction?

Answer 8

Put the polystyrene cup into a beaker of cotton wool to give more insulation and put a lid on the cup to reduce energy lost by evaporation.

Question 9

Describe an energy level diagram for an exothermic reaction.

Answer 9

The products are at a lower energy than the reactants. The difference in height represents the energy given out in the reaction(per mole)
The initial rise in the line represents the energy needed to break the old bonds, activation energy.

Question 10

Describe an energy level diagram for an endothermic reaction.

Answer 10

The products are at a higher energy than the reactants. The difference in height represents the energy being taken in during the reaction.
The initial rise in the line represents the energy needed to break the old bonds, activation energy.

Question 11

What is activation energy?

Answer 11

The minimum energy needed for the reaction to take place and to react the particles to break their bonds.

Question 12

What does a catalyst do in a chemical reaction?

Answer 12

A catalyst provides a different pathway for a reaction that had a lower activation energy so the reaction happens more easily.

Question 13

How do you calculate energy change in a chemical reaction?

Answer 13

Energy change = bonds broken - bonds formed
If it is a minus number it means it has lost energy so it is an exothermic reaction.
If it is a positive number it has gained energy so it is an endothermic reaction.

Question 14

What is useful about the reaction between oxygen and hydrogen?

Answer 14

They react to produce water which isn’t a pollutant.

The reaction is exothermic so you can get energy from it.

Question 15

How can hydrogen be use as a fuel?

Answer 15

Hydrogen can be used as a fuel by burning it in oxygen in the combustion engines of vehicles.

Question 16

What is a fuel cell?

Answer 16

A fuel cell is an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity.

Question 17

Why is a fuel cell different to a battery?

Answer 17

Unlike a battery, a fuel cell doesn’t run down or need recharging as it’ll produce energy as long as fuel is supplied.

Question 18

Advantages of fuel cells?

Answer 18

Only by-products are water and heat so they’re good for the environment.
Good for cities where air pollution from traffic is a big problem.
Help countries become less dependant on crude oil.

Question 19

Disadvantages of hydrogen fuel cells?

Answer 19

Hydrogen is a gas so it takes up more space to store than liquid fuels(like petrol)
Difficult to store safely as it’s very explosive.
The hydrogen fuel is often made from hydrocarbons which uses electricity that has to be generated by fossil fuels.

Question 20

How do you work out energy transferred in a calorimetry experiment?

Answer 20

Energy transferred(joules) =
mass of water(g) x specific heat capacity of water(4.2) x temperature change(degrees)

Q = mcT